(a) Field of the Invention
The invention relates to a communication device, particularly to a communication device that is capable of eliminating echo and crosstalk.
(b) Description of the Related Art
FIG. 1 shows a schematic diagram illustrating a communication device in the prior art. The communication device 10 comprises a transmitting medium 11, a hybrid circuit 12, a local transmitting circuit Tx, and a local receiving circuit Rx. The communication device 10 can perform signal transmission and reception with a far-end communication device via the transmitting medium 11. Generally, the local transmitting circuit Tx comprises a digital to analog (DA) converter (not shown) for converting a signal into an analog signal to generate a transmission signal STX that is then outputted through the hybrid circuit 12 and the transmitting medium 11. The local receiving circuit Rx comprises an analog to digital (AD) converter for performing analog to digital conversion on the receiving signal SRX inputted via the hybrid circuit 12 and the transmitting medium 11.
Since signal transmission and reception of the communication device 10 usually occur at the same time, while the local receiving circuit Rx of the communication device 10 receives the signal SRX from the far-end communication device, the local receiving circuit Rx is interfered by the echo bounced back from the far-end communication device after the local transmitting circuit Tx of the communication device 10 transmits a signal and also interfered by near-end cross talk (NEXT) to result in lowering communication quality of the communication system.
Furthermore, the power of the signal SRX received by the local receiving circuit Rx of the communication device 10 is reduced due to transmission distance and the local receiving circuit 13 also simultaneously receives an echo signal, the power of which is much larger than the signal SRX. In order to completely receive and process the two signals, the dynamic range of the analog to digital (AD) converter of the local receiving circuit Rx should be designed to be large. Thus, the design of the communication device becomes complicate to result in increasing production cost.